1. A person of great, mind-blowing wisdom. Usually reserved and reluctant to speak.
2. A hoopyfrood.

Taken from the David Bowie song 'Starman'.

"There's a Starman waiting in the sky
He'd like to come and meet us
But he thinks he'd blow our minds
There's a Starman waiting in the sky
He's told us not to blow it
Cause he knows it's all worthwhile."